Mainline final voltage test failed

[hryc111]

I finally finished building a Mainline kit I've had for a couple of years. All resistance and voltage checks passed except one: The final voltages at the 6.3V solder pads were ~6.3V and 0.

I saw this earlier thread: https://forums.bottlehead.com/threads/mainline-final-volt-test-fail.15621/

My finished circuit is behaving like that one at the very end of the thread, where the Zener diode was replaced with a wire.

Encouraged by that thread, I tried the amp, and it sounds great. So I guess my question is: Should I continue to troubleshoot this?

Andy H
Crack/Moreplay/Mainline

 

[Paul Birkeland]

Do you have the PT-11 in your Mainline kit? The version prior would have had the 6.3V supply grounded on one end.

The heater supply is only biased up because we do that in the Eros, which shares the same board, so you could cut out the 75K resistor and replace the zener diode with a piece of wire and there will be no negative consequences.

-PB

 

[hryc111]

PT-11 transformer, yes. PT-11 circuit board says v. 3.5. I built it as described in the manual v. 1.1 (filename with 10-08-20-y1sdl0). The supplied parts match most closely the ones in the final build photograph (which differs in some details from the pictures in the main part of the manual).

So no need to worry about this voltage result? Certainly seems to be working beautifully, although I only did one quick test.

 

[Paul Birkeland]

It's not the worst idea to at least figure out where the heater supply is being dragged to ground. Usually this happens from issues around pins 4/5 on each 6C45 socket, and pins 4/5/9 on the 12AU7 socket. Something is likely touching that shouldn't be, or the Zener diode on the power supply board is in backwards.

 

[hryc111]

Thank you so much. A fantastic kit-building experience, as always. And fantastic support. Will poke around.